part of part of in taxon capable of capable of part of contributes to morphology of regulation of heart rate cardiac muscle contraction Vertebrata <vertebrates> conducting system of heart sinoatrial node WP:Heart states: "The SA node is found in all amniotes but not in more primitive vertebrates. In these animals, the muscles of the heart are relatively continuous and the sinus venosus coordinates the beat which passes in a wave through the remaining chambers. Indeed, since the sinus venosus is incorporated into the right atrium in amniotes, it is likely homologous with the SA node. In teleosts, with their vestigial sinus venosus, the main centre of coordination is, instead, in the atrium.". Note however that ZFA has SA node. cardiac muscle of right atrium conducting tissue of heart